1. Field of the Invention
The present invention relates to a switching device of a digital amplifier and a method for controlling the same, and more particularly to a switching device of a digital amplifier and a method for controlling the same wherein a distortion occurring in a digital amplifier due to a pulse width of a PWM signal may be prevented using an MLP signal and a compensating signal.
2. Description of the Related Art
A digital amplifier also known as class D amplifier transmits an electric power by switching transistors. Since the digital amplifier is not only highly efficient but also does not need a heat sink, the digital amplifier may be easily miniaturized.
FIG. 1 is block diagram exemplifying a conventional digital amplifier.
Referring to FIG. 1, a PCM (Pulse Code Modulation) signal is converted to a PWM (Pulse Width Modulation) signal by a PWM converter 20. As shown in FIG. 2, the PWM signal has a pulse width corresponding to the amplitude of an analog signal. The PWM signal shown in FIG. 2 is a BD modulated PWM signal which has a value of +1, a value of zero or a value of −1 according to the amplitude of the analog signal.
The PWM signal is applied to and drives a switch module 30. When the PWM signal has the value of +1, the PWM converter 20 outputs a logical high as a signal P and a logical low as a signal N. On the contrary, when the PWM signal has the value of −1, the PWM converter 20 outputs the logical low as the signal P and the logical high as the signal N. When the PWM signal has the value of zero, the PWM converter 20 outputs the logical low as the signal P and the logical low as the signal N.
A signal A and a signal B outputted by the switch module 30 driven by the signal P and the signal N are passed through a low-pass filter 40 to be applied to a speaker 50. A difference between the signal A and the signal B, i.e., VDD, zero or −VDD is applied to the low-pass filter 40.
The switch module 30 is composed of semiconductors. Particularly, as shown in FIG. 1, the switch module 30 may be embodied using the plurality of semiconductors.
The semiconductors included in the switch module 30 perform switching operations according to a signal applied to a gate of the semiconductors. When the pulse width of the PWM signal applied to the gate of the semiconductors is sufficiently long, i.e., when the pulse width of the PWM signal is sufficiently longer than a switching time of the semiconductors, the semiconductors perform the switching operations normally. However, when the pulse width of the PWM signal is shorter than a predetermined length, the semiconductors cannot perform the switching operations normally resulting in a distortion of an output signal of the switch module 30.
Particularly, since the pulse width of the PWM signal is very short about a zero-crossing (shown in FIG. 2 as dotted line) of the analog signal, the distortion may occur in the output signal of the switch module 30. Therefore, a sound quality of audio signal outputted by the speaker 50 may be degraded.